Basic Concept:

The aim of UHTIMv2 is to provide a comparison of ‘Baseline’ (i.e. ‘Do Nothing’ or ‘Business As Usual’) traffic activities over a period, against ‘Sites Active’ (i.e. ‘Do Something’) activities over the same period. The ‘Baseline’ and ‘Sites Active’ are treated as separate scenarios in UHTIMv2, though calculated simultaneously during a model run. Emission calculations within the model are driven primarily by the type of vehicle (trucks generally emit more than cars for example), and the distance they have to travel (longer routes give more emissions overall).

Emissions Calculations:

Emissions from UHTIMv2 are calculated using individual Look-Up Tables (LUTs) for each specified pollutant. An individual LUT may give an emission rate as a function of:

• Pollutant
• Year;
• Vehicle type;
• Road Type;
• Road Gradient;
• Vehicle Loading, and;
• Vehicle Speed

At the lowest level LUTs are provided for individual vehicles (e.g. Petrol Car complying to the Euro 5 emission standard), but scenario calculations are generally performed on tables based on ‘fleets’ – i.e. weighted-averages (logarithmically weighted-averages in the case of noise) of the contributions from multiple types of vehicles. For 'mass-based' emissions, rates are required to be in grams per kilometer (g/km).

Obviously, using appropriate rates in the LUTs is critical for successful model operation. The TIM has been demonstrated using emissions rates and fleet data from a variety of sources, including:

• The UK Department of Environment, Food and Rural Affairs’ (DEFRA) Emissions Factor Toolkit;
• The UK Highways England Interim Advice Note ‘IAN 185/15’ model (NB: links to external PDF document);
• The UK National Atmospheric Emissions Inventory (NAEI);
• COPERT (COmputer Programme for the Emissions from Road Transport) emission factors, from EMISIA;
• The HBEFA (Handbook Emission Factors for Road Transport) from Infras.

Note that fleet data from EMISIA for COPERT, and the HBEFA are commercial products from third-parties, and therefore data from these sources isn’t included in the UHTIMv2 distribution. Rather, the data included in the download of UHTIMv2 for demonstration purposes comes from earlier versions (5.1.3) of the UK NAEI and EFT databases.

For noise, calculations are based on an approach derived from a simplified version of the EU Joint Research Centre (JRC) CNOSSOS-EU model (NB: links to external PDF document). CNOSSOS allows the calculation of sound power levels from vehicles across multiple frequency bands, and requires a complex propagation model to produce results. The (current) approach in TIM is based on using an appropriate LUT of pre-calculated A-weighted sound power levels by vehicle type and speed from CNOSSOS. These values are then used in the simplified approach proposed by Watts et al. for CNOSSOS’ predecessor model, HARMONOISE, to calculate an approximate L_Aeq sound pressure level at roadside.

For ESALs, calculations are based on axle loading and vehicle weight values extracted from Newcastle University’s PITHEM (Platform for Integrated Traffic, Health and Environmental Modelling) tool.